Preparation of organolead compounds



United States Patent ()filice 3,052,702 Patented Sept. 4, 1962 3 052 702 PREPARATION OF OTKGA NOLEAD COMPOUNDS Gene C. Robinson, Baton Rouge, La., assignor to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Jan. 5, 1959, Ser. No. 784,861 6 Claims. (Cl. 260-437) This invention relates to the preparation of organometallic compounds, particularly organolead compounds.

The present commercial process for the manufacture of organolead compounds, mainly tetraethyllead, has been practiced for more than 30 years. It is based upon the reaction of sodium-lead alloy (NaPb) with ethyl chloride. Although the process has been developed considerably over the years, an inherent disadvantage is that only A of the lead entering the reaction is consumed in the formation of the desired organolead product. The remaining 75 percent results as by-product lead which must be reprocessed to sodium-lead alloy to effect the efficiencies and economies of the comercial operation.

Attempts have been made to alleviate this problem of the large amount of by-product lead formed which has to be reprocessed and does noet result in organolead product without such reprocessing. For example, a process is described in US. Patent 2,535,193 wherein such by-product lead is further reacted with the Grignard compound, RMgX, and additional organic halide to produce the organolead product and the magnesium salt. A somewhat analogous process employing the organo compounds of lithium, zinc, and cadmium is disclosed in U.S. Patents 2,558,207; 2,562,856 and 2,591,509 respectively. While these processes have shown that the by-product lead can be further reacted to produce additional organolead compound, they have not been employed on a commercial basis because of certain disadvantages. For example, the yields employing such are not sufficient to compensate for the excessive cost of the starting material. The metal alkyl likewise is difiicult to prepare such that again the economies of their preparation are prohibitive to the realization of obtaining additional organolead product. Still further such metal alkyls are consumed in the reaction to form the corresponding metal salt so that the reformation of the metal alkyl is not readily attainable. Additionally these processes require particular solvents to effect the reaction in order to obtain satisfactory results, in particular the ethers. The utilization of such solvents further complicates the process requiring separation and recovery.

Accordingly, a more efi'icient and effective method for producing the organolead' compounds from lead metal would be highly desirable from the aspect of utilizing the by-product lead produced in the present commercial process for producing tetraethyllead and to provide a new and more eflicient process for the manufacture of organo lead compounds. Therefore, an object of this invention is to provide a new, novel and eflicient process for the manufacture of organolead compounds. Another object is to provide a process for the preparation of organolead compounds in higher yield and purity. A further object is to provide a process for the co-production of organolead compounds and another metallic compound which can be employed for regenerating the starting organometallic compound. A more specific object is to provide a process for the commercial product, tetraethyllead, while simultaneously producing triethylaluminum.

The above and other objects of this invention are accomplished by reacting lead and an organic ester of an inorganic acid with a bimetallic organometallic compound, wherein one metal is selected from the group consisting of group I-A and IIA metals and the other metal is selected from the group consisting of IIB and III-A metals.

The bimetallic compounds in which one metal is a group IA metal, especially sodium, and the other metal is a group IIA metal, especially aluminum, and the organo portion is alkyl having up to about 8 carbon atoms are particularly preferred because of their greater availability and reactivity. The organic halides, especially ethyl chlo ride, are preferred esters. Although the temperature at which the reaction can be conducted is subject to considerable latitude, it is preferred to operate at temperatures between about 25 to C. Thus, in a particularly preferred embodiment of this invention sodium tetraethylalminum is reacted with lead metal and ethyl chloride at a temperature between about 25 to 150 C. to produce tetraethyllead. A by-product of the process of this invention is the formation and co-production of a compound of the group IIA or IIIA metals which is of considerable use. For example, in the reaction of sodium tetraethyl-aluminum with lead and ethyl chloride, aluminum triethyl is also co-produced.

The process of this invention consistently results in higher yield and purity of organolead compound than heretofore obtainable based upon the lead metal employed. A particular advantage is that in addition to the formation of the organolead product, the process results in a by-product metallic compound which is readily recycled to form the starting bimetallic organometallic compound employed in the process. In other words, this material is in effect constantly regenerated, either in situ or by external reaction, thereby resulting in a conservation of the organometallic compound employed and its only consumption being toward the formation of the desired organolead product. A still further advantage of the process is that the distinct bimetallic organometallic compounds are readily obtained and are either liquid or soluble in the most economical organic solvents. Additionally, whereas the prior art techniques have required the use of only the organic iodides in the reaction of lead with the organometallic compound or the employment of iodide including organic iodide as catalysts, the present process proceeds readily regardless of the organic halide employed and in the absence of the idodie catalyst. Hence, the most economical organic chlorides are applicable and such are preferred. Still further advantages of the present process will be evident as the discussion proceeds.

In general any bimetallic organometallic compound can be employed. The most suitable of such compounds are those wherein one metal is selected from the group consisting of group IA and IIA metals and the other metal is selected from the group consisting of group IIB and IIIA metals. The bimetallic organometallic compound must, in general, have at least one carbon to metal bond and the unsatisfied valences can be satisfied with .organic radicals and other ligands which are essentially inert in the reaction. Such materials may be depicted by the following formula:

wherein M is a group I-A or IIA metal; M is preferably a group IIB or III-A metal or metalloid; Y is an organic radical, preferably hydrocarbon, having up to and including about 18 carbon atoms; Y is another ligand including electron donating ligands, as for example, the halogens, organic radicals, preferably hydrocarbon having up to and including 18 carbon atoms, alcohol residues having up to and including about 18 carbon atoms, and hydrogen; a is a small whole number from 1 to 4 inclusive, b can be 0 to 3 inclusive, and c is equivalent to the valence of M. Typical examples of such compounds include sodium tetraethylaluminum, sodium tetraoctylaluminum, sodium tetraoctadecylaluminum, sodium tetravinylaluminum, sodium tetracyclohexylaluminum, sodium tetraphenylaluminum, sodium tetrabenzylaluminum, sodium tetranaphthyl aluminum, sodium triethylaluminum hydride, sodium diethylaluminum dihydride, sodium ethylaluminum triethoxide, sodium diethylaluminum diethoxide, sodium triethylaluminum chloride, sodium diethylaluminum dichloride, sodium triethylzinc, sodium trioctyl zinc, sodium diethylzinc hydride, sodium diethylzinc chloride, sodium diethylzinc iodide, and similar such compounds wherein lithium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, or barium are substituted for sodium and boron, gallium, indium, thalilium, cadmium and mercury are substituted for aluminum and zinc. The fully alkylated bimetallic compounds in which the organic radicals are hydrocarbon alkyl radicals having up to about 8 carbon atoms are especially preferred, particularly those wherein M is sodium and M is aluminum or boron because of their greater availability, higher reactivity and superior physical characteristics which contribute toward ease of handling, greater yields and liquid phase reaction systems.

The organic esters of inorganic acids are compounds which are capable of contributing an organic radical wherein a carbon atom will bond to the lead metal. In this sense they can also be termed hydrocarbylating agents. It is to be understood that this terminology embodies not only the formation of alkyllead compounds, but also aryl, cycloalkyl, and the like and, in general, both aliphatic and aromatic lead compounds. Such materials can be depicted by the formula wherein at least one of said Rs is an organic radical, preferably hydrocarbon alkyl, and the other can be the aforementioned organic radicals or hyrogen, Z is an anion which is bonded with the aforementioned R groups, and a is a small whole number from 1 to 2 inclusive. The preferred Z groups comprise the sulfate, phosphate and halogen anions derived from the corresponding inorganic acids. Included among such materials are for example ethyl chloride; ethyl bromide; ethyl iodide, butyl chloride, bromide and iodide; octyl chloride, bromide and iodide; decyl chloride, bromide and iodide; octadecyl chloride, bromide and iodide; vinyl chloride; cyclohexyl chloride; phenyl chloride, ethynyl chloride; benzyl chloride; naphthyl chloride; and the like and similar such compounds wherein the anion is the phosphate or sulfate anion as for example diethyl sulfate, ethyl ethane sulfonate, sodium ethyl sulfate, ethyl p-toluene sulfonate, dioctyl sulfate, triethyl phosphate, trioctadecyl phosphate and the like. The alkylating and arylating agents are preferred esters or hydrocarbylating agents. The alkylating agents which are organic halides, particularly the hydrocarbon halides having up to about 18 carbon atoms, are

especially preferred because of their greater availability and reactivity. In an especially preferred embodiment the alkyl chlorides having up to and including 8 carbon atoms are generally employed because of the higher yields obtained and their more practical application.

The lead metal which is employed can be in any form but is preferably in the finely divided state. Generally particle sizes below about 4; inch major dimensions are preferred. Such metal can be obtained either by mechanical methods or chemical methods. Mechanical methods involving grinding or shaving lead metal are applicable and chemical methods wherein lead metal is precipitated or deposited in finely divided form are also applicable.

Thus, examples of lead which can be successfully employed include lead powders resulting from the decomposition of organolead compounds by heat, such as for instance, the lead deposited during the thermal decomposition of organolead compounds. Certain other forms of lead powders which are applicable for use in making organolead can be prepared by grinding or otherwise comminuting lead metal or massive lead, especially when this is done in an atmosphere of nitrogen or under an appropriate liquid, which prevents the oxidation of the lead surface. A further example of a method of preparing a finely divided lead suitable for practicing the invention is the reductive precipitation of lead from its compounds. Other methods, such as electrolytic deposition, will occur to those skilled in the art.

.Lead alloys, particularly alloys containing alkaline earth and alkali metals, are also a good source of lead and have been successfully employed. Sodium-lead alloy is an especially good alloy for such use. Other examples of metals alloyed with the lead which can be successfully used in practicing the invention are calcium, potassium and magnesium. In general, any alloy which will react in the following equation can be employed as a source of lead:

Metal-lead alloy+ethyl chloride =tetraethyllead+leadl-metal chloride The process of this invention will be more completely understood from a consideration of the following examples. In each instance, all parts are by weight.

Example I To an autoclave equipped with external heating means and agitation, which was precooled to 70 C., was added 16.99 parts of sodium-lead alloy (NaPb) in a sealed glass bulb and 70 parts of ethyl chloride were added thereto and the reactor sealed. The reaction mixture was preheated to C. and agitated thereby breaking the glass bulb. The mixture was reacted at these conditions for 3 hours and cooled to 20 C. Then 20 parts of sodium tetraethylaluminum were added thereto along with 20 parts of ethyl chloride. The autoclave was again sealed and the reaction mixture was heated and agitated at 70-80" C. for 3 hours. Then 40 parts of isopropyl alcohol were added to kill by-product triethylaluminum compound. A portion of the reaction product was subjected to analysis for tetraethyllead. The yield of tetraethyllead, based upon the lead employed, was 68.2 percent.

Example II When 10.47 parts of byproduct and lead obtained from the reaction of 14.96 parts of sodium-lead alloy with 70 parts of ethyl chloride at 80 C. for 3 hours, were reacted with 10 parts of sodium tetraethylaluminum and 70 parts of ethyl chloride at 80-85 C. for 3 hours, the yield of tetraethyllead, based on the sodium tetraethylaluminum, was 76.4 percent.

Example III In this run 12 parts of reagent lead powder and 10 parts of sodium tetraethylaluminum were added to the reactor. The reactor was cooled to a 7() C., and then 70 parts of ethyl chloride were fed to the reactor. The reactor was sealed and heated to 8090 C. with agitation. This temperature was then maintained for a total of 3 hours. The reactor was then cooled to 70" C. and about 40 parts of isopropyl alcohol were added to kill the triethylaluminum by-product. A yield of 17.3 percent of tetraethyllead was obtained.

When lead shot was substituted in the above example, similar results were obtained.

Example IV Finely divided lead, 12.82 parts, obtained as a by-prodnot from the reaction of sodium-lead alloy with ethyl chloride were added to an autoclave along with 20 parts of sodium tetraethylbo-ron in 14 parts of diethyl ether and the mixture heated to 70 C. Then 43 parts of ethyl chloride were fed over a peniod of 20 minutes.

The reaction mixture was then cooked for an additional 3 hours at autogenous pressure and then vented. Then the by-product, triethylborane, was extracted with aqueous caustic and tetraethyllead was recovered therefrom. It was found that 8.46 parts of tetraethyllead were obtained representing a yield of 66 percent based upon the 12.82 parts of lead employed.

When the above example was repeated employing sodium tetraethylaluminum in place of the boron compound, all other conditions being the same, the yield of ethyllead compound was 89.5 percent. Substituting tetrahydrofuran for diethyl ether and again employing sodium tetraethylaluminum, the yield of ethyllead product was 93.7 percent. Substituting hexane for diethyl ether and sodium tetraethylaluminum for the boron compound, the yield was 54.3 percent.

Example V In this instance, 10.42 parts of sodium tetraethylaluminum were placed in a reactor with 87 parts of toluene along with 6.76 parts of finely divided lead. Agitation was commenced and the mixture heated to the reflux temperature. Then 10.52 parts of diethyl sulfate in 26 parts of toluene were addded over a period of 1 hour. The reaction mixture was maintained at reflux for an additional 1 hour period, then about 40 parts of isopropyl alcohol were added to kill triethylaluminum by-product. Tetraethyllead was recovered in high yield.

Example VI Example I is repeated essentially as described except that at the completion of the reaction no alcohol is added to kill the unreacted by-product aluminum compounds. Instead the reaction mixture is filtered and then subjected to fractional distillation to separate the tetraethyllead from the triethylaluminurn by-product and the latter is also recovered in high yield.

Example VII Employing the procedure of Example I, 10.75 parts of finely divided lead were placed in the reactor along with 8.1 parts of sodium triethylzinc in 43 parts of dimethoxyethane. The reactor was cooled to '-70 C. and then 70 parts of ethyl chloride were added thereto and the reactor sealed. The reactor was then heated to 80 C. and agitated. These conditions were maintained for a period of 3 hours. At the end of this time, the reactor was cooled and tetraethyllead was recovered in a yield of 29.1 percent. The diethyl zinc by-product can be recovered from the reaction mixture if desired.

Example VIII In this run 40 parts of lead metal of particle size below inch are reacted with 20 parts of lithium aluminum tetraphenyl and triphenyl phosphate at 150 C. for 4 hours. Tetraphenyllead is obtained in high yield along with triphenyl aluminum.

' Example IX Employing the procedure of Example III, 10 parts of finely divided lead are reacted with 12 parts of magnesium aluminum ethyl compound [Mg(AlEt and ethyl bromide. An essentially quantitative conversion to tetraethyllead is obtained along with a high recovery of triethylaluminum.

Example X Again employing the procedure of Example III, tetracyclohexyllead and tricyclohexyl aluminum are recovered in high yield when lead is reacted with sodium tetracyclohexylaluminum and cyclohexyl chloride at 25 C. for 3 hours.

Example XI Example IV is repeated with exception that sodium triethylaluminum hydride is substituted for sodium borotetraethyl in the absence of a solvent and the reaction temperature is maintained at C. for 3 hours. Tetr-aethyllead is obtained in high yield along with diethylaluminum hydride.

Example XII Employing the procedure of Example HI, finely divided lead metal is reacted with sodium trioctylaluminum chloride and octyl chloride at 25 C. for 4 hours to produce tetraoctyl lead and dioctyl aluminum chloride.

Example XIII In this run 5 parts of potassium aluminum tetrabenzyl and 6 parts of finely divided lead metal are added to the reactor and the reaction temperature raised to 65 C. Then 20 parts of benzyl chloride are fed over a period of /2 hour. The mixture is then cooked for an additional 1 hour period at this temperature and the autogenous pressure. Upon cooling and filtering the liquid phase is then fractionally distilled to separate tetrabenzyl lead from the tribenzyl aluminum by-product and residual benzyl chloride.

Example XIV Employing the procedure of Example III, lead metal is reacted with sodium diethylaluminum diethoxide and ethyl chloride at C. and 100 p.s.i. for 1 hour. Tetraethyllead is obtained in high yield along with ethyl diethoxy aluminum.

It is not necessary that the organo groups on the bimetallic organometallic compound be symmetrical nor that they be identical to those of the organic esters. The following example will demonstrate the use of dissimilar organic radicals in these materials resulting in organolead product having dissimilar alkyl groups attached.

Example XV When 12.7 parts of lead, by-product obtained from the reaction of sodium-lead alloy with ethyl chloride, were reacted with 20 parts of sodium tetraethylaluminum in 9.1 parts of diethyl ether and 70 parts of methyl bromide for 3 hours at 70 C. and the organolead product recovered and analyzed by vapor phase chromatography, it Was found that the product comprised 49 percent tetraethyllead, 28 percent methyl triethyllead, 9 percent dimethyldiethyl-lead, 8 percent ethyltrimethyl lead and 6 percent tetramethyllead. The yield of such a mixture of organolead products was 77.5 precent.

The above examples have been presented by way of illustration and it is not intended that the invention be limited thereto. It will be evident that the bimetallic organometallic compounds and the organic esters discussed previously can be substituted in the above examples to produce similar results.

In general, the reaction conducted according to the process of this invention is self-sustaining and can be initiated at temperatures as low as about 20 C. and as high as about 200 C. and higher depending upon the decomposition temperature of the products. It is prefer- ,able to employ a temperature between about 25 to C. to avoid side reaction and excessive decomposition ,of the products. If desired, thermal stabilizers which are well known to the art can be employed when higher temperatures are used as for example naphthalene, styrene, anthracene and the like. Although the process will proceed at subatmospheric, atmospheric and superatrnospheric pressure, it is generally desirable to maintain some pressure in the system when highly volatile organic esters are employed such as MeCl and EtCl.

The reaction time employed can likewise be varied over a considerable range. Generally not more than about 20 hours reaction time is required and less than 6 hours is desirable to avoid excessive exposure of the product at the higher temperatures which will result in some decomposition. In a particularly preferred embodiment between about /2 to 4 hours reaction time is used.

In general, diluents or solvents are not required in the process but can be used to advantage for heat distribution and solvating in those instances when the bimetallic organometallic compound is a solid. The organic solvents which are essentially inert under the reaction conditions and liquid are applicable. For such purposes the hydrocarbons, ethers, and tertiary amines have been found most suitable. Among the hydrocarbons are included both aliphatic and aromatic materials as, for example, the hexanes, octanes, nonanes, cyclohexanes, benzene, toluene, xylene, tetralin and the like. The ethers include, for example, diethyl ether, diamyl ether, dioctyl ether, methylamyl ether, diphenyl ether, dibenzyl ether, cyclic ethers, such as dio-xane, tetrahydrofuran and the polyethers as, for example, the dimethyl, diethyl, dibutyl and the like ethers of ethylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol. In cluded among the amines are the primary, secondary and tertiary amines, especially the tertiary amines which are less reactive with the bimetallic organometallic compound. Typical examples of such amines include ethyl, butyl and octyl amine, diethyl amine, dibutyl amine, dicyclohexyl amine, diphenyl amine, dibenzyl amine, triethyl amine, triphenyl amine, aniline, pyridine and isoquinoline. While many of the ethers and amines will complex with the bimetallic oranometallic compound, this does not prevent their use in the reaction. The aromatic hydrocarbons, cyclic ethers, polyethers and tertiary amines comprise a preferred group of diluents to be employed because of their greater availability and easier recovery from the reaction system. The cyclic ethers and polyethers, especiallytetrahydrofuran and the dimethyl, diethyl and methyl ethyl ethers of diethylene glycol are particularly preferred because of their greater solubility for the bimetallic organometallic compounds and their reaction promoting effect.

The proportions of the reactants are not critical and are based upon the amount of lead metal employed in the reaction. The bimetallic organometallic compound is generally employed between about 0.5 to stoichiometric equivalents as set forth in the above typical equation per mole of the lead metal. The organic ester is generally between about 0.5 to stoichiometric equivalents per mole of the lead metal. In an especially preferred embodiment between about 1 to 4 stoichiometric equivalents of the bimetallic organometallic compound and between about 6 to 10 stoichiometric equivalents of the organic ester per mole of lead are employed to result in high yield and eflicient utilization of the starting materials. When an excess of organic ester is employed, such is readily recoverable from the reaction system.

When a diluent is employed, it is generally present in amount sufiicient to provide fluidity of the reaction mixture. Generally between about 1 part to 100 parts per part by weight of lead metal is employed.

The principal product produced according to the process of this invention, namely the organolead products, are well known and of considerable utility as, for example, antiknock agents. The commercial product, tetraethyllead, is extensively used for this purpose as an additive to fuels for internal combustion engines. The byproduct organometallic compound is useful in regenerating the bimetallic organometallic compound or in the preparation of other organometallics. For example, triethylaluminum can be reacted with mercury chloride to produce ethyl mercury chloride. Likewise, tn'ethylaluminum is useful in the formation of catalysts for the polymerization of ethylene. These and other uses of the products of this invention will be evident to those skilled in the art.

Having thus described the process of this invention, it is not intended that it be limited except as set forth in the following claims.

I claim:

1. A process for the manufacture of hydrocarbon lead compounds which comprises reacting finely divided lead and an organic ester selected from the group consisting of a hydrocarbon sulfate, hydrocarbon phosphate, and hydrocarbon halide wherein said hydrocarbon groups have up to and including 18 carbon atoms with a bimetallic organometallic compound wherein one metal is selected from the group consisting of group I-A and II-A metals, the other metal is different from said first metal and selected from the group consisting of group II-B and III-A metals, and said bimetallic orgauometallic compound has at least one carbon to metal bond of a hydrocarbon group having up to and including 18 carbon atoms and the remaining unsatisfied valences of said bimetallic organometallic compound are satisfied by moieties selected from the group consisting of said hydrocarbon groups having up to and including 18 carbon atoms, the halogens, and alkoxide radicals having up to and including about 18 carbon atoms.

2. The process of claim 1 wherein said organic ester is a hydrocarbon halide having up to about 18 carbon atoms in the hydrocarbon group, and said bimetallic organometallic compound is a fully alkylated compound wherein the organic groups are hydrocarbon alkyl having up to about 8 carbon atoms, one metal is sodium, and the other metal is selected from the group consisting of boron and aluminum.

3. The process of claim 2 wherein the reaction is conducted at a temperature between about 25 to C. in the presence of an ether.

4. A process for the manufacture of. tetraethyllead which comprises reacting sodium aluminum tetraethyl with finely divided lead and ethyl chloride at a temperature between about 25 to 150 C.

5. The process of claim 4 further characterized in that the reaction is conducted in the presence of tetrahydrofuran.

6. The process of claim 4 further characterized in thgt the reaction is conducted in the presence of diethyl et er.

References Cited in the file of this patent UNITED STATES PATENTS 2,859,229 Blitzer et al. Nov. 4, -8 2,863,894 Smith Dec. 9, 1958 FOREIGN PATENTS 548,439 Belgium Dec. 7, 1956 

1. A PROCESS FOR THE MANUFACTURE OF HYDROCARBON LEAD COMPOUNDS WHICH COMPRISES REACTING FINELY DIVIDED LEAD AND AN ORGANIC ESTER SELECTED FROM THE GROUP CONSISTING OF A HYDROCARBON SULFATE, HYDROCARBON PHOSPHATE, AND HYDROCARBON HALIDE WHEREIN SAID HYDROCARBON GROUPS HAVE UP TO AND INCLUDING 18 CARBON ATOMS WITH A BIMETALLIC ORGANOMETALLIC COMPOUND WHEREIN ONE METAL IS SELECTED FROM THE GROUP CONSISTING OF GROUP I-A AND II-A METALS, THE OTHER METAL IS DIFFERENT FROM SAID FIRST METAL AND SELECTED FROM THE GROUP CONSITING OF GROUP II-B AND III-A METALS, AND SAID BIMETALLIC ORGANOMETALLIC COMPOUND HAS AT LEAST ONE CARBON TO METAL BOND OF A HYDROCARBON GROUP HAVING UP TO AND INCLUDING 18 CARBON ATOMS AND THE REMAINING UNSATIFIED VALENCES OF SAID BIMETALLIC ORGANOMETALLIC COMPOUND ARE SATISFIED BY MOETIES SELECTED FROM THE GROUP CONSISTING OF SAID HYDROCARBON GROUPS HAVING UP TO AND INCLUDING 18 CARBON ATOMS, THE HALOGENS, AND ALKOXIDE RADICALS HAVING UP TO AND INCLUDING ABOUT 18 CARBON ATOMS. 